Precambrian geology of the Arseno Lake map area, District of Mackenzie, Northwest Territories

The Arseno Lake map area lies mostly within the Wopmay Oro gen which comes into contact with the western margin of the Slave Structural Province. The Proterozoic rocks in the area consist chiefly of Snare Group rocks of the Coronation Supergroup. These rocks were folded, metam01phosed and intruded by granites of the Hepburn Intrusive Suite during Wopmay orogenesis. Domes of Archean basement gneiss were emplaced into the Snare Group during this orogeny. Structures in the Snare Group and in the Slave Craton suggest that the bulk of the Proterozoic and Archean rocks west of the Slave Province boundary are allochthonous and were derived from the west along sole faults that coincide with the presently defined Slave Province boundary. The basement-cored gneiss domes and supracrustal rocks in the western part of the Proterozoic allochthon have been metamorphosed to granulite facies and consist mostly of rust coloured biotite gneiss and schist derived from rocks of subgreywacke composition. Intraformational quartz pebble conglomerates serve as marker beds in this succession, outlining a complex structural history dominated by east-west compression.followed by subsequent uplift of the gneiss domes. Toward the Slave Province margin the proportion of coarse elastic rocks decreases and siltstone, argillite, quartzite, calc-silicate rocks and dolomite are common. The Snare Group is folded in this area into tight steeply-dipping, gently north-plunging inclines that verge eastward. Archean deformation is recognized in the Slave Province where metasedimentary rocks were folded into-northwest-to northerly-trending isoclinal structures, and the more homogeneous metavolcanic and granitoid rocks were horizontally compressed and foliated. Proterozoic deformation further compressed Archean structures near the western margin of the Slave Craton, evidenced by south- to southwest-plunging structures similar to those in the gneiss dome areas and in the allochthonous Snare Group, and by younger structures associated with the development of the isoclinally folded Snare Group rocks near the Slave boundary. Granulite facies metammphism in the southernmost gneiss dome area grades down to greenschist facies near the contact with the Slave Province. This metam01phism is associated with Wopmay orogenesis, although its centre occurred farther west. Regional isograds developed during the orogeny were transported eastward with the thrusting of the sedimentary prism onto the Slave Craton. Low-grade Proterozoic retrograde metamorphism overprints Archean "Kenoran" metammphic textures and has reset some K-Ar and Rb-Sr mineral and whole rock systems along the margin of the Slave Province.